Re: Black Holes in the Big Rip

OwlHoot wrote:
If the expansion of the Universe is accelerating, as recent
observations indicate, and this continues, then eventually
space will be expanding at faster than light speed in a
vacuum (the so-called "Big Rip").

This is wrong in a couple of ways. First, the rate of expansion of space doesn't have units of speed and hence can't exceed c. Space is already expanding "faster than light" in some sense: the comoving relative speed of opposite ends of the visible universe is around 7c. Second, the Big Rip doesn't refer to exponential expansion but to a different scenario in which the scale factor goes to infinity in a finite time. This only happens if the dark energy density increases with time. If the dark energy behaves like a cosmological constant (constant density everywhere in spacetime), then eventually it dominates the expansion and you get what's effectively a de Sitter vacuum. The universe is still perfectly inhabitable in this phase; it becomes impossible to see or travel to other galaxies, but nothing gets ripped apart.

-- Ben

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